Oil seal

ABSTRACT

An oil seal ( 1 A) has an outer member ( 2 ) fitted to a crankcase ( 100 ), an inner member ( 3 ) integrally rotatably fitted to a crankshaft ( 101 ), and a first movable lip ( 4 ) disposed in the gap (G 1 ) formed by the outer member ( 2 ) and the inner member ( 3 ). The first movable lip ( 4 ) is disposed such that it is not in contact with the outer member ( 2 ) when rotation of the crankshaft ( 101 ) is stopped and that it is displaced in the direction to approach the outer member ( 2 ), coming into contact with the outer member ( 2 ) to close the gap (G 1 ).

TECHNICAL FIELD

The present invention relates to an oil seal disposed between astationary body and a rotation body which is rotatably attached to thestationary body.

RELATED ART

Some oil seal which prevents leakage of fluid such as oil is providedwith a movable floating ring in a prescribed gap between a rotation bodyand a stationary body, and is provided with a lip seal which is incontact with the stationary body to close the prescribed gap whenrotation of the rotation body is stopped (Patent document 1).

[Patent document 1] JP2004-A-132524

SUMMARY OF INVENTION Problems to be Solved by the Invention

In the oil seal of Patent document 1, the lip seal is displaced bycentrifugal force in the direction to be separated from the stationarybody as the rotational speed of the rotation body increases, thestationary body and the lip seal change from the state they are incontact with each other to the state they are not in contact with eachother. Accordingly, frictional resistance between the stationary bodyand the lip seal is reduced. However, when the stationary body and thelip seal get in the state they are not in contact with each other as therotational speed of the rotation body increases, leakage of oil may beprovoked since the gap closed by the lip seal is opened.

Thus, it is an object of the present invention to provide an oil sealcapable of preventing leakage of oil due to increase of the rotationalspeed of a rotation body.

Means of Solving Problems

In order to solve the above problem, the oil seal according to thepresent invention is an oil seal disposed between a stationary body anda rotation body which is rotatably attached to the stationary body; andincludes an outer member fitted to the stationary body; an inner memberwhich is integrally rotatably fitted to the rotation body and isassembled together with the outer member such that a prescribed gap isformed between the inner member and the outer member; and a movablemember which is disposed in the prescribed gap, wherein the movablemember is provided to the inner member such that it is not in contactwith the outer member when rotation of the rotation body is stopped andthat it is displaced in the direction to approach the outer member,coming into contact with the outer member to close the prescribed gap asthe rotational speed of the rotation body increases.

According to this oil seal, the movable member that is not in contactwith the outer member when rotation of the rotation body is stopped isdisplaced in the direction to approach the outer member, and comes intocontact with the outer member as the rotational speed of the rotationbody increases. Accordingly, frictional resistance is reduced, since theouter member is not in contact with the movable member until the movablemember comes into contact with the outer member. Since the prescribedgap is closed after the movable member comes into contact with the outermember, leakage of oil dues to the increase of the rotational speed ofthe rotation body can be prevented reliably.

In the oil seal of the present invention, the movable member may beprovided with a pressure receiving part which receives pressure in theinternal space of the stationary body and urges the movable member inthe approaching direction. According to this aspect, since the pressurereceiving part receives pressure in the internal space, the movablemember is urged in the direction to approach the outer member. Thus,sealing effect of the movable member of closing the prescribed gap isimproved, since the movable member can be pressed against the outermember by using pressure in the internal space. In this aspect, thepressure receiving part may have a skirt which comes into contact withthe outer member when the movable member comes into contact with theouter member. In this case, since the skirt facilitates the pressurereceiving part to receive pressure in the internal space, the movablemember can be pressed more strongly against the outer member.Furthermore, the skirt also comes into contact with the outer member,when the movable member comes into contact with the outer member.Accordingly, the contact between the movable member and the outer memberbecomes more tightly, and thus the sealing effect is improved further.

In the oil seal of the present invention, the gap between the movablemember and the outer member may be provided such that labyrinth sealable to suppress leakage of oil is formed between the movable member andthe outer member when the movable member is not in contact with theouter member. According to this aspect, even when the movable member isnot in contact with the outer member, leakage of oil is suppressed bythe labyrinth seal which is formed of the outer member and the movablemember. Accordingly, leakage of oil can be prevented effectively overthe speed range from a low rotational speed of the rotation body beforethe prescribed gap is closed by the movable member to a high rotationalspeed of the rotation body after the prescribed gap is closed by themovable member, without increasing number of parts.

In the oil seal of the present invention, the oil seal of the presentinvention may further include another movable member which is disposedin the prescribed gap, wherein the another movable member is provided tothe inner member such that the another movable member is in contact withthe outer member and the prescribed gap is closed when rotation of therotation body is stopped, and the another movable member is displaced inthe direction to be separated from the outer member such that theprescribed gap gets opened as the rotational speed of the rotation bodyincreases. According to this aspect, by properly setting thedisplacement characteristics of the two movable members, respectively,the characteristics of the oil seal can be flexibly adjusted accordingto required characteristics.

In the oil seal of the present invention, a floating ring which ismovable in no contact with both the outer member and the inner membermay be disposed in the prescribed gap. According to this embodiment,labyrinth seal can be formed easily without setting the narrow width ofthe prescribed gap. Accordingly, leakage of oil can be preventedeffectively over the speed range from a low rotational speed of therotation body before the prescribed gap is closed by the movable memberto a high rotational speed of the rotation body after the prescribed gapis closed by the movable member, without increasing the frictionalresistance.

In the oil seal of the present invention, the movable member may have acontact part which comes into contact with the outer member; and thecontact part may be formed of low friction material having lowerfriction coefficient than that of the other parts thereof. Furthermore,the outer member may have a contact part which comes into contact withthe movable member; and the contact part may be formed of low frictionmaterial having lower friction coefficient than that of other partsthereof. In these cases, the resistance to pressure of the oil seal isimproved, since the movable member can be pressed more strongly againstthe outer member while suppressing the increase of the frictionalresistance.

In a case that the movable member has such a contact part, the contactpart may have a low friction region formed of low friction material andan elastic region formed of elastic material having lower stiffness thanthat of the low friction material. The low friction region and theelastic region may be disposed respectively on the contact part suchthat, as the rotational speed of the rotation body increases, themovable member changes from the state the low friction region of themovable member is in contact with the outer member but the elasticregion of the movable member is not in contact with the outer member tothe state that both the low friction region and the elastic region ofthe movable member are in contact with the outer member. According tothis aspect, the frictional resistance between the outer member and themovable member can be reduced when the outer member is in contact withthe low friction region but the outer member is not in contact with theelastic region. Then, when the rotational speed of the rotation bodyincrease further than that state, pressure in the internal space of thestationary body increases, however; sealing characteristics is improvedsince the outer member is in contact with both the low friction regionand the elastic region. Accordingly, leakage of oil can be reliablyprevented, for example, even when pressure in the internal space 100becomes extraordinarily high for any reason. At the same time, intrusionof foreign matter from outside can be prevented, too.

Furthermore, the outer member may be provided with an auxiliary elasticpart which opposes to the contact part of the movable member and may beformed of elastic material having lower stiffness than that of theconstituent material of the outer member. The movable member may bedisplaced such that the contact part comes into contact with theauxiliary elastic part as the rotational speed of the rotation bodyincreases. In this case, sealing characteristics is improved when themovable member is in contact with the outer member with the auxiliaryelastic member interposed therebetween, since the auxiliary elastic partis formed of elastic material having lower stiffness than that of theconstituent material of the outer member. Furthermore, since theauxiliary elastic part is provided to the stationary outer member, theincrease of the weight of the movable member can be avoided. Thus,sealing characteristics can be improved while keeping the response ofthe movable member.

In the oil seal of the present invention, the another movable member mayhave a contact part which comes into contact with the outer member, andthe contact part may be formed of low friction material having lowerfriction coefficient than that of the other parts thereof. According tothis aspect, the frictional resistance between the another movablemember and the outer member can be reduced before the another movablemember is separated from the outer member.

In this aspect, the contact part may have a low friction region formedof the low friction material and an elastic region formed of the lowfriction material having lower stiffness than that of the low frictionmaterial. The another movable member may be provided to the inner membersuch that the outer member is in contact with both the low frictionregion and the elastic region when rotation of the rotation body isstopped. When the contact part of the another movable member is fullyformed of low friction material, the reducing effect of friction isimproved, however; sealing characteristics is easily degraded due to theinfluence of axial runout or the like at a low rotational speed beforethe another movable member gets separated from the outer member, sinceit is hard to be deformed. According to this aspect, since the outermember is in contact with both the low friction region and the elasticregion before the another movable member gets separated from the outermember, such degradation of the sealing characteristics can becompensated, and frictional force can be reduced further than the casewhen the contact part is fully formed of elastic material.

In the oil seal of the present invention, a crankcase of an internalcombustion engine may be provided as the stationary body, and acrankshaft of the internal combustion engine may be as the rotationbody. According to this aspect, since the movable member is in contactwith the outer member and the prescribed gap is closed even when theinternal pressure in the crankcase becomes higher than atmosphericpressure due to the increase of load at a high speed rotation of thecrankshaft, leakage of oil and blow-by gas in the crankcase can bereliably prevented

EFFECT OF INVENTION

As described above, according to the present invention, the movablemember, which is not in contact with the outer member when rotation ofthe rotation body is stopped, is displaced in the direction to approachthe outer member and comes into contact with the outer member as therotational speed of the rotation body increases. Since the prescribedgap is thus closed, leakage of oil due to the increase of the rotationalspeed of the rotation body can be prevented.

BRIEF DESCRIPTION OF DRAWINGS

[FIG. 1] FIG. 1 is a schematic cross-sectional view showing a main partof an internal combustion engine to which an oil seal according to thefirst embodiment of the present invention is applied.

[FIG. 2] FIG. 2 is a view showing the oil seal of FIG. 1 when thecrankshaft is in a rotating state.

[FIG. 3] FIG. 3 is a view showing the oil seal of FIG. 1 when therotational speed of the crankshaft is faster than that in FIG. 2.

[FIG. 4] FIG. 4 is a schematic cross-sectional view showing a main partof an internal combustion engine to which an oil seal according to thesecond embodiment of the present invention is applied.

[FIG. 5] FIG. 5 is a view showing the oil seal of FIG. 4 when thecrankshaft is rotating.

[FIG. 6] FIG. 6 is a schematic cross-sectional view showing a main partof an internal combustion engine to which an oil seal according to thethird embodiment of the present invention is applied.

[FIG. 7] FIG. 7 is a schematic cross-sectional view showing a main partof an internal combustion engine to which an oil seal according to thefourth embodiment of the present invention is applied.

[FIG. 8] FIG. 8 is a schematic cross-sectional view showing a main partof an internal combustion engine to which an oil seal according to thefifth embodiment of the present invention is applied.

[FIG. 9] Fig .9 is a view showing the oil seal of FIG. 8 when thecrankshaft is rotating.

[FIG. 10] FIG. 10 is a schematic cross-sectional view showing a mainpart of an internal combustion engine to which an oil seal according tothe sixth embodiment of the present invention is applied.

[FIG. 11] FIG. 11 is a view showing the oil seal of FIG. 10 when thecrankshaft is rotating.

[FIG. 12] FIG. 12 is a view showing the oil seal of FIG. 10 when therotational speed of the crankshaft is faster than that in FIG. 11.

[FIG. 13] FIG. 13 is a schematic cross-sectional view showing a mainpart of an internal combustion engine to which an oil seal according tothe seventh embodiment of the present invention is applied.

[FIG. 14] FIG. 14 is a view showing the oil seal of FIG. 13 when thecrankshaft is rotating.

[FIG. 15] FIG. 15 is a schematic cross-sectional view showing a mainpart of an internal combustion engine to which an oil seal according tothe eighth embodiment of the present invention is applied.

[FIG. 16] FIG. 16 is a view showing the oil seal of FIG. 15 when thecrankshaft is rotating.

[FIG. 17] FIG. 17 is a view showing the oil seal of FIG. 15 when therotational speed of the crankshaft is faster than that in FIG. 16.

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment

FIG. 1 is a schematic cross-sectional view showing a main part of aninternal combustion engine in which an oil seal according to the firstembodiment of the present invention is installed. It is noted that onlya half of a cross section will be shown in FIG. 1 and other figures,since the oil seal according to the present invention is axiallysymmetric with respect to the axis CL. FIG. 1 shows a state of acrankshaft 101 when rotation is stopped, and the crankshaft 101 isattached to a crankcase 100 in a rotatable manner around the axis CL.The oil seal 1A is disposed between the crankcase 100 and the crankshaft101, wherein the crankcase 100 serves as a stationary body and thecrankshaft 101 serves as a rotation body. Namely, the oil seal 1A isfitted in an annular gap formed between the crankcase 100 and thecrankshaft 101. The oil seal 1A separates an atmospheric side AS outsidethe crankcase 100 from a hermetically sealed side OS inside thecrankcase 100, thereby to prevent the leakage of fluid such as oil andblow-by gas from the hermetically sealed side OS to the atmospheric sideAS and to prevent intrusion of foreign matter such as dust from theatmospheric side AS to the hermetically sealed side OS. The oil seal 1Ahas an annular outer member 2 provided coaxially with the crankshaft 101and an annular inner member 3, respectively. The outer member 2 isfitted to the crankcase 100 with the oil seal retainer 103 interposedtherebetween, whereas the inner member 3 is integrally rotatably fittedto the crankshaft 101. The outer member 2 and the inner member 3 areassembled together with a separation from each other, such that a gap Gis formed between them.

The outer member 2 has an outer cylinder 21 which is fixed to the oilseal retainer 103 and extends in the direction of the axis CL; and aninward flange 22 which extends radial inwardly from the end of the outercylinder 21 at the atmospheric side AS. The inward flange 22 includes avertical wall 22 a which rises up radial inwardly and substantialvertically with respect to the outer cylinder 21; an inclined wall 22 bwhich continues to the vertical wall 22 a and is inclined toward thehermetically sealed side OS; and a side wall 22 c which continues to theinclined wall 22 b and extends in the direction of the axis CL. On theother hand, the inner member 3 has an internal cylinder 31 which isfixed to the crankshaft 101 and extends in the direction of the axis CL;and an outward flange 32 which extends radial outwardly from the end ofthe internal cylinder 31 at the hermetically sealed side OS. The outwardflange 32 is disposed so as to oppose to the inward flange 22 of theouter member 2. Namely, the outward flange 32 includes a vertical wall32 a which rises up radial outwardly and substantially vertically withrespect to the internal cylinder 31 and is substantially parallel to thevertical wall 22 a of the inward flange 22; a side wall 32 c whichcontinues to the vertical wall 32 a and extends in the direction of theaxis CL and is substantially parallel to the side wall 22 c of theinward flange 22; and an inclined wall 32 b which continues to the sidewall 32 c and extends so as to be inclined toward the atmospheric sideAS and is substantially parallel to the inclined wall 22 b of the inwardflange 22.

Among the gap G's formed between the outer member 2 and the inner member3, an annular first movable lip 4 which serves as a movable member isdisposed in the gap G1 formed between the side wall 22 c of the inwardflange 22 and the internal cylinder 31 of the inner member 3. The firstmovable lip 4 is formed of elastic material such as rubber, and has abase end 4 a attached to the end of the internal cylinder 31 at thehermetically sealed side OS; a middle part 4 b which extends from thebase end 4 a toward the atmospheric side AS; and a tip end 4 c which isfolded back radial outwardly from the middle part 4 b toward. An annulargarter spring 7 which urges the first movable lip 4 radial inwardly isattached to the tip end 4 c. In the state shown in FIG. 1 that rotationis stopped, the first movable lip 4 is kept in no contact with the outermember 2, that is, in the state the gap G1 is opened by the elasticforce of the garter spring 7.

Furthermore, among the gap G's formed between the outer member 2 and theinner member 3, an annular second movable lip 5 which serves as anothermovable member is disposed in the gap G2 formed between the side wall 22c of the inward flange 22 and the side wall 32 c of the outward flange32. The second movable lip 5 is formed of elastic material such asrubber in the same manner as the first movable lip 4. The second movablelip 5 has a base end 5 a which is attached to at the boundary betweenthe vertical wall 32 a of the outward flange 32 and the side wall 32 c;a middle part 5 b which extends from the base end 5 a toward theatmospheric side AS; and a tip end 5 c which is folded back radialinwardly from the middle part 5 b. An annular garter spring 8 for urgingthe second movable lip 5 radial inwardly is attached to the tip end 5 c.In the state shown in FIG. 1 that rotation is stopped, the secondmovable lip 5 is pressed against the outer member 2 by the elastic forceof the garter spring 8, and is kept in a state the gap G2 is closed bythe second movable lip 5.

Furthermore, among the gap G's formed between the outer member 2 and theinner member 3, a floating ring 9 is disposed in the gap G3 formedbetween the inclined wall 22 b of the inward flange 22 and the inclinedwall 32 b of the outward flange 3. The floating ring 9 can move in thegap G3 in no contact with the outer member 2 and the inner member 3,respectively, while the crankshaft 101 is rotating. Namely, the floatingring 9 is structured to rotate concentrically with the inner member 3 ata slower speed than the circumferential velocity of the inner member 3while the oil existing in the gap G3 is interposed between the floatingring 9 and the outer member 2 and between the floating ring 9 and theinner member 3, respectively. By considering the width of the gap G3,the thickness of the floating ring 9 is set such that labyrinth sealsare formed between the three members of the floating ring 9, the outermember 2, and the inner member 3.

FIG. 2 and FIG. 3 show the oil seal 1A when the crankshaft 101 is in arotating state; and FIG. 3 shows a state the rotational speed of thecrankshaft 101 is faster than that in the state of FIG. 2. Since theinner member 3 rotates integrally with the crankshaft 101 when thecrankshaft 101 rotates, radial outwardly oriented centrifugal forceexerts on the first movable lip 4. The centrifugal force increases inproportion to the rotational speed of the crankshaft 101. Thus, alongwith the rotational speed of the crankshaft 101 increases, the firstmovable lip 4 is displaced in the direction to approach the outer member2, and the first movable lip 4 comes into contact with the outer member2 as shown in FIG. 3. Accordingly, the gap G1 is closed by the firstmovable lip 4. Such behavior of the first movable lip 4 according to thevariation in the rotational speed of the crankshaft 101 can becontrolled freely, for example, by setting the specification such as anouter diameter and a spring constant of the garter spring 7 and theconstituent material of the first movable lip 4 properly. For example,the first movable lip 4 can be structured so as to come into contactwith the outer member 2 at an arbitrary targeted rotational speed of thecrankshaft 101.

Furthermore, the radial outwardly oriented centrifugal force exerts alsoon the second movable lip 5 disposed in the gap G2 due to the rotationof the crankshaft 101. As a result of the increase of the centrifugalforce as the rotational speed of the crankshaft 101 increases, the forceof pressing the second movable lip 5 against the outer member 2decreases gradually. Then, the second movable lip 5 is displaced in thedirection of leaving from the outer member 2 as shown in FIG. 2, so thatthe gap G2 is opened. In the same manner as the first movable lip 4, thebehavior of the second movable lip 5 can also be structured such thatthe second movable lip 5 is separated from the outer member 2 at anarbitrary targeted rotational speed of the crankshaft 101, by settingthe specification such as an outer diameter and a spring constant of thegarter spring 8 and the constituent material of the second movable lip 5properly.

Second Embodiment

Next, the second embodiment of the present invention will be describedwith h reference to FIG. 4 and FIG. 5. The oil seal 1B according to theembodiment has the same structure as that of the oil seal 1A of thefirst embodiment except for the structure of the first movable lip 204which serves as a movable member. In FIG. 4 and FIG. 5, the samecomponents as in the first embodiment have the same reference numbers.In the following, the duplicated description with the first embodimentwill be omitted.

The oil seal 1B has an annular first movable lip 204 formed of elasticmaterial such as rubber; and the first movable lip 204 includes a baseend 204 a attached to the internal cylinder 31 of the inner member 3, amiddle part 204 b which extends from the base end 204 a toward thehermetically sealed side OS, and a tip end 204 c which is folded backradial outwardly from the middle part 204 b. In the oil seal 1B, whenthe first movable lip 204 is displaced in the direction to approach theouter member 2 as the rotational speed of the crankshaft 101 increases,the inner circumference surface 210 of the first movable lip 204 turnstoward the hermetically sealed side OS as shown in FIG. 5. When pressurein the internal space 100 a of the crankcase 100 (pressure at thehermetically sealed side OS) is higher than atmospheric pressure, thepressure exerts on the inner circumference surface 210 of the firstmovable lip 204, so that the first movable lip 204 receives the pressureand is urged in the direction to approach the outer member 2. Thus, thesealing effect of the first movable lip 204 is improved, since the firstmovable lip 204 can be pressed against the outer member 2 by utilizingthe pressure in the internal space 100 a. Accordingly, the innercircumference surface 210 of the first movable lip 204 works as thepressure receiving part of the present invention.

Third Embodiment

Next, the third embodiment of the present invention will be describedwith reference to FIG. 6. The oil seal 1C according to this embodimentis that of the second embodiment in which a skirt 11 is provided to theinner circumference surface 210 of the first movable lip 204, andcorresponds to a variation of the oil seal 1B. In the following and inFIG. 6, the same components as in the second embodiment have the samereference numbers, and the duplicated description will be omitted. Theskirt 11 of the oil seal 10 extends from the first movable lip 204toward the hermetically sealed side OA. The skirt 11 is structured suchthat the tip end thereof comes into contact with the outer member 2 whenthe first movable lip 204 comes into contact with the outer member 2 asshown in FIG. 6 with the solid line. It is noted that when thecrankshaft 101 stops rotating, the first movable lip 204 is kept in nocontact with the outer member 2 as shown in FIG. 6 with broken line.According to this embodiment, since it gets easy to receive the pressurein the internal space 100 a of the crankcase 100 when the skirt 11 isprovided, the first movable lip 204 can be pressed more strongly againstthe outer member 2 by using the pressure. Thus, the sealing effect ofthe first movable lip 204 is further improved than in the secondembodiment. In the oil seal 10, the inner circumference surface 210 ofthe first movable lip 204 and the skirt 11 work as the pressurereceiving part of the present invention.

Fourth Embodiment

Next, the fourth embodiment of the present invention will be describedwith reference to FIG. 7. The oil seal 1D according to this embodimenthas an annular first movable lip 404 which is formed of elastic materialsuch as rubber. The first movable lip 404 has a base end 404 a attachedto the internal cylinder 31 of the inner member 3, and is structured soas to extend from its base end 404 a toward the hermetically sealed sideOS. Unlike the above-mentioned embodiments, no garter spring is attachedto the first movable lip 404 at its tip end. Namely, the first movablelip 404 is kept in no contact with the outer member 2 by its own elasticforce as shown in FIG. 7 with broken line, when the crankshaft 101 stopsrotating. Then, when the rotational speed of the crankshaft 101increases, the centrifugal force generated along with the rotationovercomes the elastic force of the first movable lip 404, and thus thefirst movable lip 404 is displaced in the direction to approach theouter member 2 as shown in FIG. 7 with the solid line, and comes intocontact with the outer member 2. Since the structure of the firstmovable lip 404 is more simplified than those in the above-mentionedembodiments it can contribute to the reduction of cost. The innercircumference surface 410 of the first movable lip 404 of thisembodiment turns toward the hermetically sealed side OS, when the firstmovable lip 404 is displaced in the direction to approach the outermember 2. Thus, in the same manner as the second and the thirdembodiments, the inner circumference surface 410 can press the firstmovable lip 404 against the outer member 2 by utilizing the pressure inthe internal space 100 a of the crankcase 100; and the innercircumference surface 410 works as the pressure receiving part of thepresent invention. Nevertheless, the orientation along which the firstmovable lip 404 extends may be opposite to that in FIG. 7. Namely, inthe same manner as the first embodiment, it may be structured so as toextend from the base end 404 a toward the atmospheric side AS.

Fifth Embodiment

Next, the fifth embodiment of the present invention will be describedwith reference to FIG. 8 and FIG. 9. As shown in FIG. 8, the oil seal 1Eaccording to this embodiment has an annular outer member 502 providedcoaxially with the crankshaft 101 and an inner member 503, respectively.The outer member 502 is fitted to the crankcase 100 via the oil sealretainer 103, whereas the inner member 503 is integrally rotatablyfitted to the crankshaft 101. In the same manner as the above-mentionedembodiments, the outer member 502 and the inner member 503 are assembledtogether with a separation from each other, such that a gap G is formedbetween them.

The outer member 502 has an outer cylinder 521 which is fixed to the oilseal retainer 103 and extends in the direction of the axis CL; and aninward flange 522 which extends radial inwardly from the end of theouter cylinder 521 at the atmospheric side AS. The inward flange 522includes an inclined wall 522 a which is inclined from the end of theouter cylinder 521 at the atmospheric side AS toward the atmosphericside AS; a horizontal wall 522 b which continues to the inclined wall522 a and extends radial inwardly; and a side wall 522 c which continuesto the horizontal wall 522 b and extends in the direction of the axisCL. On the other hand, the inner member 503 has an internal cylinder 531which is fixed to the crankshaft 101 and extends in the direction of theaxis; and an outward flange 532 which extends radial outwardly from theend of the internal cylinder 31 at the hermetically sealed side OS. Theoutward flange 532 has an inclined wall 532 a which is inclined form theend of the internal cylinder 531 at the hermetically sealed side OStoward the hermetically sealed side OS; a horizontal wall 532 b whichcontinues to the inclined wall 532 a and extends radial outwardly; and aside wall 532 c which continues to the horizontal wall 532 b and extendsin the axial direction.

Among the gap G's formed between the outer member 502 and the innermember 503, an annular first movable lip 504 which serves as movablemember is disposed in the gap G1 formed between the inclined wall 522 aof the inward flange 522 and the side wall 532 c of the outward flange532. The first movable lip 504 is formed of elastic material such asrubber, and has a base end 504 a attached to the end of the outwardflange 532 of the side wall 532 c at the atmospheric side AS. The firstmovable lip 504 is structured so as to extend from the base end 4 a insubstantially parallel to the inclined wall 522 a of the inward flange522. In the same manner as the fourth embodiment, no garter spring isattached to the tip end of them. Accordingly, the first movable lip 504is kept in no contact with the outer member 502 by its own elastic forceas shown in FIG. 8, when the crankshaft 101 stops rotating. Then, whenthe rotational speed of the crankshaft 101 increases, the centrifugalforce generated due to the rotation overcomes the elastic force of thefirst movable lip 504, and thus the first movable lip 504 is displacedin the direction to approach the outer member 502 and comes into contactwith the outer member 502 as shown in FIG. 9. In the same manner as thesecond to the fourth embodiments, the inner circumference surface 510 ofthe first movable lip 504 turns toward the hermetically sealed side OSwhen the first movable lip 504 is displaced in the direction to approachthe outer member 502. Accordingly, the inner circumference surface 510of the first movable lip 504 receives the pressure in the internal space100 a of the crankcase 100, and can urge the first movable lip 504 inthe direction to approach the outer member 502. Thus, the innercircumference surface 510 of the movable lip 504 works as the pressurereceiving part of the present invention.

Among the gap G's formed between the outer member 502 and the innermember 503, an annular second movable lip 505 which serves as anothermovable member is disposed in the gap G2 formed between the side wall522 c of the inward flange 522 and the side wall 532 c of the outwardflange 532. The second movable lip 505 has the same structure as that ofthe second movable lip of each of the above-mentioned embodiments. Whenthe crankshaft 101 stops rotating, the second movable lip 505 is pressedagainst the outer member 502 by the elastic force of the garter spring 8and is kept in a state the gap G2 is closed by the second movable lip505 as shown in FIG. 8. Then, when the rotational speed of thecrankshaft 101 increases, the second movable lip 505 is displaced by thecentrifugal force generated due to the rotation in the direction ofleaving from the outer member 502 as shown in FIG. 9, so that the gap G2is opened.

In this embodiment, the contact part 12 on which the first movable lip504 comes into contact with the outer member 502 is formed of lowfriction material having lower friction coefficient than that of otherparts thereof (the first movable lip 504). As the low friction material,for example, fluorine resin such as polytetrafluoroethylene (PTFE) anddiamond like carbon (DLC) can be used. Accordingly, since the frictionalresistance due to the contact is reduced when the outer member 502 is incontact with the first movable lip 505, leakage of oil can be reliablyprevented while suppressing the increase of loss of torque. The contactpart 13 of the second movable lip 505 is also formed of low frictionmaterial in a same way. Furthermore, the outer member 502 which is incontact with the first movable lip 504 and the second movable lip 505can be formed of the above-mentioned low friction material. Namely, thecontact part of the outer member 502 which is contact with the firstmovable lip 504 or the second movable lip 505 may be formed of the lowfriction material. It is noted that the contact part of the movable lipaccording to any of the above-mentioned embodiments can be formed of theabove-mentioned low friction material.

Furthermore, in this embodiment, the gap g between the first movable lip504 and the outer member 2 is set such that a labyrinth seal capable ofsuppressing leakage of oil is formed between the first movable lip 504and the outer member 2 when the first movable lip 504 and outer member 2are not in contact with each other. The width of the gap g is setproperly according to the pressure which can be generated in theinternal space 100 a of the crankcase 100. Thus, even when the firstmovable lip 504 is not in contact with the outer member 502, leakage ofoil is suppressed by the labyrinth seal formed by the outer member 502and the first movable lip 504. Accordingly, in the same manner as theabove-mentioned embodiments, leakage of oil can be prevented effectivelyover the speed range from a low rotational speed of the crankshaft 101before the gap G1 is closed by the first movable lip 504 to the highrotational speed of the crankshaft 101 after the gap G1 is closed by thefirst movable lip 504 without providing with a separate part such as afloating ring and without increasing number of parts.

Sixth Embodiment

Next, the sixth embodiment of the present invention will be describedwith reference to FIG. 10 to FIG. 12. The sixth embodiment correspondsto a variation of the fifth embodiment. The common parts between thesixth embodiment and the fifth embodiment have the same referencenumbers in these figures; and the duplicated description will beomitted. As shown in these figures, the oil seal 1F includes a firstmovable lip 604, which serves as a movable member and has a contact part14 that comes into contact with the outer member 502. The contact part14 of the first movable lip 604 has a low friction region 14 a formed ofthe above-mentioned low friction material having lower frictioncoefficient than that of the other parts thereof; and an elastic region14 b formed of elastic material having lower stiffness than that of thelow friction material. The low friction region 14 a is disposed at thetip end side of the first movable lip 604, whereas the elastic region 14b is disposed at the side of a base end 604 a of the first movable lip604, these regions are adjacent to each other. The elastic region 14 bhas lower stiffness than the low friction region 14 a and is deformedeasily. Thus, when the elastic region 14 b is in contact with the outermember 502, the sealing characteristics is better than when the lowfriction region 14 a is in contact with the outer member 502. It isnoted that the rubber made from polyamide or the like is suited for theelastic material.

When the rotational speed of the crank shaft 101 increases, the oil seal1F changes from the state of FIG. 10 to the state of FIG. 11. In thestate of FIG. 11, the first movable lip 604 is displaced to a positionwhere the outer member 502 is in contact with the low friction region 14a of the contact part 14 but the outer member 502 is not in contact withthe elastic region 14 b of the contact part 14. Then, when therotational speed of the crank shaft 101 increases further from the stateof FIG. 11, the movable lip 604 is displaced to a position where theouter member 502 is in contact with both the low friction region 14 aand the elastic region 14 b as shown in FIG. 12.

According to this embodiment, resistance to friction can be reduced whenthe low friction region 14 a is in contact with the outer member 502 inthe state of FIG. 11. When the rotational speed of the crank shaft 101increases further than that of FIG. 11, the pressure in the internalspace 100 a of the crankcase 100 increases, however; sealingcharacteristics is improved since the outer member 502 is in contactwith both the low friction region 14 a and the elastic region 14 b asshown in FIG. 12. Thus, leakage of oil can be reliably prevented, forexample, even when the pressure in the internal space 100 a of thecrankcase 100 becomes extraordinarily high for any reason. At the sametime, intrusion of foreign matter from outside can also be prevented. Itis noted that the inner circumference surface 610 of the first movablelip 604 also serves as the pressure receiving part of the presentinvention.

Seventh Embodiment

Next, the seventh embodiment of the present invention will be describedwith reference to FIG. 13 and FIG. 14. The seventh embodimentcorresponds to a variation of the fifth embodiment. The common partsbetween the seventh embodiment and the fifth embodiment have the samereference number in these figures; and the duplicated description willbe omitted. As shown in these figures, the oil seal 1G has a secondmovable lip 705 which serves as another movable member having a contactpart 15 which comes into contact with the outer member 502. The contactpart 15 of the second movable lip 705 has a low friction region 15 aformed of the above-mentioned low friction material having lowerfriction coefficient than the other parts of the second movable lip 705and an elastic region 15 b formed of elastic material having lowerstiffness than that of the low friction material. These regions areplaced side-by-side. Before the second movable lip 705 is separated fromthe outer member 502 as shown in FIG. 13, for example, when the crankshaft 101 stops rotating, the second movable lip 705 is provided to theinner member 503 such that the outer member 502 is in contact with boththe low friction region 15 a and the elastic region 15 b. When therotational speed of the crank shaft 101 increases, the second movablelip 705 gets in a separated state from the outer member 502 as shown inFIG. 14.

Since the variation in torque is large and axial runout is also large ata low rotational speed before the second movable lip 705 is separatedfrom the outer member 502 or when rotation is stopped, the secondmovable lip 705 is easily separated from the outer member 502. When thecontact part 15 is fully formed of low friction material, the reducingeffect of friction is improved, however; their sealing characteristicsare easily degraded at a low rotational speed when axial runout or thelike tends to occur. In this embodiment, since the outer member 502contacts with both the low friction region 15 a and the elastic region15 b, the degradation of the sealing characteristics can be compensatedand the frictional force can be reduced further than the case when thecontact part 15 is fully formed of elastic material. It is noted thatthis embodiment can be embodied in combination with the sixth embodimentshown in FIG. 10.

Eighth Embodiment

Next, the eighth embodiment of the present invention will be describedwith reference to FIG. 15 to FIG. 17. The eighth embodiment correspondsto a variation of the fifth embodiment. The common parts between theseventh embodiment and the fifth embodiment have the same referencenumbers in these figures; and the duplicated description will beomitted. As shown in these figures, the outer member 502 of the oil seal1H is provided with an auxiliary elastic part 16 which opposed to thecontact part 12 of the first movable lip 504. The auxiliary elastic part16 is formed in an annular shape and is formed of elastic materialhaving lower stiffness than that of the constituent material of theouter member 502. In order to contact with the first movable lip 504more tightly, the elastic member 16 is structured in a form having awedge shape cross section such that it becomes gradually thinner towardradial outwardly. Since the auxiliary elastic part 16 is formed ofelastic material having lower stiffness than that of the constituentmaterial of the outer member 502, the sealing characteristics areimproved further in a case when it contacts with the outer member 502with the auxiliary elastic member 16 interposed than the case when thecontact part 12 contacts with the outer member 502 itself.

When the rotational speed of the crank shaft 101 increases, the oil seal1H changes from the state of FIG. 15 to the state of FIG. 116. In thestate of FIG. 15, the first movable lip 504 is displaced to a positionwhere the outer member 502 is contact with the contact part 12 but theouter member 502 is not contact with the auxiliary elastic part 16.Then, when the rotational speed of the crank shaft 101 increases furtherfrom the state of FIG. 16, the movable lip 504 is displaced to theposition where the contact part 12 contact with the auxiliary elasticpart 16 as shown in FIG. 17.

In this embodiment, frictional resistance can be reduced, when thecontact part 12 contact with the outer member 502 in the state of FIG.16. When the rotational speed of the crank shaft 101 increases furtherthan the state of FIG. 16, the pressure in the internal space 100 a ofthe crankcase 100 increase, however; since the contact part 12 is incontact with the auxiliary elastic part 16 as shown in FIG. 17, thesealing characteristics is improved. Accordingly, even when the pressurein the internal space 100 a of the crankcase 100 becomes extraordinarilyhigh for any reason, for example, leakage of oil can be reliablyprevented. At the same time, intrusion of foreign matter from outsidecan be prevented, too. Furthermore, since the auxiliary elastic part 16is provided to the stationary outer member 502, increase of the weightof the first movable lip 504 can be avoided. Thus, the sealingcharacteristics can be improved while keeping the response of the firstmovable lip 504. It is noted that this embodiment can be embodied incombination with the sixth embodiment shown in FIG. 10 or the seventhembodiment shown in FIG. 13. Furthermore in this embodiment, theauxiliary elastic part 16 may be disposed such that the contact part 12comes into contact with the auxiliary elastic part 16 without goingthrough the state of FIG. 17 when the first movable lip 504 is displacedas the rotational speed of the crank shaft 101 increases.

The present invention is not limited to the above-mentioned embodiments;and it can be embodied in various forms within the spirit and scope ofthe present invention. For example, the oil seal according to thepresent invention can be also applied to various pumps in addition tothe internal combustion engine. In a case that the oil seal according tothe present invention is applied to a pump, the oil seal according tothe present invention may be disposed between a pump housing whichserves as the stationary body and a pump shaft rotatable attached to thepump housing.

Furthermore, the second movable lip is not an essential part in theabove embodiments; and the present invention may be embodied in anembodiment in which the second movable lip is omitted. Even in thiscase, the first movable lip comes into contact with the outer member asthe rotational speed of the rotation body increases, so that the gap isclosed, leakage of oil along with the increase of rotational speed ofthe rotation body can be prevented.

1-13. (canceled)
 14. An oil seal disposed between a stationary body anda rotation body which is rotatably attached to the stationary body,comprising: an outer member fitted to the stationary body; an innermember which is integrally rotatably fitted to the rotation body and isassembled together with the outer member such that a prescribed gap isformed between the inner member and the outer member; and a movablemember which is disposed in the prescribed gap, wherein the movablemember is provided to the inner member such that it is not in contactwith the outer member when rotation of the rotation body is stopped andthat it is displaced in the direction to approach the outer member,coming into contacts with the outer member to close the prescribed gapas the rotational speed of the rotation body increases, wherein themovable member has a contact part which comes into contact with theouter member, and is formed of material having lower frictioncoefficient than that of other parts of thereof, the contact part has alow friction region formed of the low friction material and an elasticregion formed of elastic material having lower stiffness than that ofthe low friction material, and the low friction region and the elasticregion are disposed respectively on the contact part such that, as therotational speed of the rotation body increases, the movable memberchanges from the state the low friction region of the movable member isin contact with the outer member but the elastic region of the movablemember is not in contact with the outer member to the state both the lowfriction region and the elastic region of the movable member are incontact with the outer member.
 15. An oil seal disposed between astationary body and a rotation body which is rotatably attached to thestationary body, comprising: an outer member fitted to the stationarybody; an inner member which is integrally rotatably fitted to therotation body and is assembled together with the outer member such thata prescribed gap is formed between the inner member and the outermember; and a movable member which is disposed in the prescribed gap,wherein the movable member is provided to the inner member such that itis not in contact with the outer member when rotation of the rotationbody is stopped and that it is displaced in the direction to approachthe outer member, coming into contacts with the outer member to closethe prescribed gap as the rotational speed of the rotation bodyincreases, wherein the movable member has a contact part which comesinto contact with the outer member, and is formed of material havinglower friction coefficient than that of other parts of thereof, theouter member is provided with an auxiliary elastic part which opposes tothe contact part of the movable member and is formed of elastic materialhaving lower stiffness than that of the constituent material of theouter member, and the movable member is displaced such that the contactpart comes into contact with the auxiliary elastic part as therotational speed of the rotation body increases.
 16. The oil sealaccording to claim 14, wherein the movable member is provided with apressure receiving part which receives pressure in the internal space ofthe stationary body and urges the movable member in the direction toapproach.
 17. The oil seal according to claim 16, wherein the pressurereceiving part comprises a skirt which comes into contact with the outermember when the movable member comes into contact with the outer member.18. The oil seal according to claim 14, further comprising anothermovable member which is disposed in the prescribed, gap, wherein theanother movable member is provided to the inner member such that theanother member is in contact with the outer member and the prescribedgap is closed when rotation of the rotation body is stopped, and theanother movable member is disposed in the direction to be separated fromthe outer member such that the prescribed gap gets opened as therotational speed of the rotation body increases.
 19. The oil sealaccording to claim 14, wherein a crankcase of an internal combustionengine is provided as the stationary body, and a crankshaft, of theinternal combustion engine is provided as the rotation body.